The invention relates to a method for manufacturing lightweight shaped concrete articles, such as block-shaped concrete building elements, flat or channel shaped insulation plates for roof sheeting purposes etc., in which substantially sphere-shaped particles of foamed plastic material are blended with a binder by means of which the adherence of the foamed plastic material to cement is promoted, at the end of which blending operation a portion of the cement in dry condition is added and co-blended with said blend until the mass again consists mainly of loose spheres, whereupon the remaining portion of the cement is added and the entire mixture is subjected again to a second mixing operation, while metering a quantity of water, and the mixture thus finally obtained is pressed into the desired shape. A method of this type is known from Dutch patent application No. 71,13658.
In the known method the binder comprises a bituminous product, i.e., a petroleum-based product. This product has the disadvantage that is smells heavily so that the articles finally obtained have to be left exposed to the open air for a long time before these articles, in particular block-shaped building elements, can be used for building, e.g. houses.
Moreover, the bituminous product has to be heated in the temperate and frigid climatic zones, before this product can be mixed with the spheres of foamed plastic material. This requires an additional operation and additional energy, while in hot climatic zones, the bituminous product does not harden and thus cannot be used.
In European patent application No. 80901389, it is proposed to use, instead of a solely bituminous product, a mixture of a bituminous product and waterglass as the binder. However, the added quantity of waterglass presents the serious disadvantage that it becomes very rapidly so viscous that the mixing apparatus will jam and that, when the apparatus is stopped after a running period, it forms such hard deposits that the apparatus cannot be started any more.
U.S. Pat. No. 3,899,455 discloses a method for preparing lightweight concrete in which closed cell foamed polystyrene particles are coated, prior to their incorporation into the concrete, with a phenol-containing coal tar. Phenol is an undesirable substance since it injuriously affects the health of the persons involved in the preparation of the concrete.
Further, in said U.S. patent it is mentioned that it is known in the art to treat the foamed particles with an aqueous dispersion of an epoxy resin prior to their incorporation into the hydraulic binding agent.
However, using an aqueous dispersion of an epoxy resin in the method according to the invention would be very detrimental to the adherence of the first portion of the cement added at the end of the first blending operation to the foamed spheres as this cement would then be set by the water contained in said dispersion. Moreover, an epoxy resin cured from an aqueous dispersion is very brittle and exhibits a poor cohesion.